The present invention relates to fire safety devices, and more particularly to thermally actuated sprinklers commonly used in commercial and residential buildings.
Large numbers of thermally-actuated fire sprinklers are installed in structures every year. These sprinklers, generally installed in the structure's ceiling, are connected to a pressurized water supply and are intended to release the water into the room when the temperature in the room indicates that a fire or conflagration is taking place.
Multiple techniques have been used to actuate prior art fire sprinkler heads. Some prior art sprinkler valves bond two components together with alloys that melt at low temperatures. When heated above the melting temperature of the eutectic alloy, the bond between the two components is released, and a control valve is permitted to open. This type of actuator is subject to failure as the solder ages and crystallizes, thereby weakening the bond.
A second type of prior art sprinkler valve uses a sealed glass tube nearly filled with a liquid that boils at a low temperature. As ambient temperature increases, the liquid boils, thereby raising the pressure inside the tube. At a high enough temperature the tube ruptures, permitting the sprinkler valve to open. Premature failure may occur, however, if the sprinkler head is subjected to mechanical shock and the tube is cracked.
Yet other prior art sprinkler valves incorporate shape memory components that change shape when a transition temperature is reached to actuate the sprinkler valve. Some such thermally actuated valves are described in U.S. Pat. No. 4,176,719; U.S. Pat. No. 4,549,717; U.S. Pat. No. 4,596,483; U.S. Pat. No. 4,706,758; U.S. Pat. No. 4,848,388; U.S. Pat. No. 4,896,728; U.S. Pat. No. 5,117,916; U.S. Pat. No. 5,494,113; U.S. Pat. No. 5,622,225; U.S. Pat. No. 5,924,492; U.S. Pat. No. 6,073,700; U.S. Pat. No. 6,840,329; and U.S. Pat. No. 6,843,465. However, these devices do not typically control the transition temperature of the shape memory alloy, and the valve structures may therefore be less reliable and overly complex.
False triggering of sprinkler heads can cause damage that is expensive to repair and contributes to the cost of fire insurance. Thermally-actuated fire safety devices must meet strict codes.
A common failure mode for fire sprinklers is the failure of the valve to open even after the trigger mechanism has removed the detent that holds the valve poppet in place. This may result from low pressure in the fluid supply line, corrosion of one or more of the parts that form the seal, or deterioration of the seal, such that the force from the fluid supply line is too small to move the poppet and open the flow path. Conventional fire sprinkler valve release mechanisms cannot be used to force open the valve, since they do not have the excess stroke and force necessary. Furthermore, shape memory alloy actuator mechanisms previously described are typically not designed to force the valve open. The majority of these designs rely on fluid pressure to move the poppet and allow flow.
Described herein are thermally-activated, frangible sprinkler valves including a shape-memory element that may meet these codes and address many of the problems identified above.